Teens: Decade of innocence
Runners in the throes of puberty have superpowers. A British study compared 12 boys and 13 men doing 10 sets of 10-second sprints. The boys sustained their power output better than the men, partly because teens regenerate creatine (a compound that supplies muscles with energy) quicker than older runners. Also, levels of lactate, the by-product of intense efforts, are naturally lower at this age.
Girls share the same ability to crank up the power - and can sustain it even better than boys. Japanese researchers found that in a series of sprints, teenage girls lost 10 per cent less power than boys the same age did. That said, as muscle mass piles on, boys have the distinct upper hand - or in this case, leg. "Proportionately, boys develop more muscles than girls do and have a natural power advantage," says Professor Cameron Blimkie of McMaster University in Canada.
Bones are still developing, too, and running helps make them as dense as possible. Blimkie's study on the bone density of female runners, triathletes, cyclists and swimmers found that runners had the highest bone-mineral density and strength.
You may be fit, but your growing body still needs to be handled with care. Bones develop faster than their supporting ligaments and tendons. As a result, joints and muscles can be prone to injury. "Some teenage female athletes get a condition called amenorrhea, which is when their regular periods stop. This can have significant implications," says Dr Jo Wallace, a lecturer in exercise physiology at Aberystwyth University. "It happens when they're training hard but aren't consuming enough calories. This causes their oestrogen levels to drop, leading their periods to stop. This can be serious, as oestrogen is needed to build healthy bones. But once girls with amenorrhea start to have a sufficient food intake, the periods will return as normal."
Wallace advises both girls and boys to not take on too much mileage, and points out that if they do get an injury, should give themselves enough recovery time: "When bones are still growing at this age, the tiny microfractures that occur naturally are increased through exercise. For most people, this is a good thing as it increases bone density in preparation for later life, when they start to deteriorate. But at this young age, there's the risk that microfractures can develop into hairline fractures, which can then turn into more serious injuries."
Work on building your form and endurance so you can become a balanced, injury-free runner further down the road. Practise sprint-specific drills such as high knees and skips to build a strong foundation, ideally under a coach's supervision. "If an athlete has good form during the early years, that helps so much with performance and injury prevention later," says coach Greg McMillan (mcmillanrunning.com). Boost aerobic capacity by upping long runs by five minutes weekly. Go by minutes, not miles - and when in doubt, take it slowly. "Not every training run should end with your hands on your knees," McMillan says.
"For healthy bone development, calcium-rich foods such as milk, yoghurt and cheese, together with exercise such as running, will build up the peak bone density for later in life," says Wallace. "But you also need to maintain sufficient energy levels for the activity you are doing by eating your protein and carbs too. Remember that your metabolism will increase as you do more exercise.
"Calories are important for maintaining fat levels, and fats help release the fat-soluble vitamins A, D, E and K, which are essential for the repair of body cells."
18, from Coventry
"I've been running since I was seven years old. When I was 11 I joined Coventry Godiva Harriers, where coaching made me faster. I went on to win the English Schools' intermediate 800m title twice, and in 2008 I was invited to join the Aviva-sponsored On Camp With Kelly mentoring and education initiative, led by Kelly Holmes.
"In my GB vest at last year's IAAF World Youth Championships I won a bronze medal and set my 800m PB (2:03.83).
"I had a setback this season when I damaged my ankle by twisting it badly while training - but it's been my first injury, and I'm getting back into it now.
"I normally train six times a week with more mileage work in the winter and more quality speed sessions in the summer. Even after a tough session, I feel fine the next day - as long as I've had a good night's sleep."